The high octane requirements of aviation gas for use in piston driven aircraft which operate under severe requirements, e.g., aircraft containing turbo charged piston engines require that commercial aviation fuels contain a high performance octane booster. The organic octane boosters for automobile gasolines (Mogas) such as benzene, toluene, xylene, methyl tertiary butyl ether, ethanol and the like are not capable by themselves of boosting the motor octane number (MON) to the 98 to 100 MON levels required for aviation gasolines (Avgas). Tetraethyl lead (TEL) is therefore a necessary component in high octane Avgas as an octane booster. However, environmental concerns over lead and its compounds may require the phasing out of lead in Avgas.
U.S. Pat. No. 2,819,953 describes aromatic amines added to motor gasolines as antiknock agents. However, motor gasolines have much lower octane requirements than aviation gasolines for piston driven aircraft. One cannot predict performance of a given antiknock agent in an aviation gasoline based on its performance as an antiknock agent in a motor gasoline.
U.S. Pat. No. 1,605,663 describes the addition of aniline to kerosene or gasoline motor fuels of the 1920's to increase the critical compression pressure of the fuel. The aniline can be added as such or mixed with other substances such as amyl alcohol, amyl acelate and orthotoluidine. When added to automobile engine fuel, the critical compression pressure may be increased to a point between the normal critical compression pressure of the untreated fuel and 160 or more pounds. The patent recites that the invention can be employed in aircraft construction by treating the common forms of aviation gasoline (of the 1920's) which were employed at the time in engines having a compression pressure of about 125 pounds to permit the increase of the compression pressure of the aircraft engines and thus increase their efficiency. In addition to aniline, other amino compounds are recited including xylidine, orthotoluidine, meta toluidine, cumidine, monopropyl aniline, mono-butyl aniline.
U.S. Pat. No. 1,592,953 describes the treatment of motor fuels such as kerosene and gasoline by adding a knock suppressing substance to increase the critical compression pressure of the fuel. The knock suppressing substance is employed in the form of a pellet or pill. The patent describes a pill or pellet of a 50/50 mixture of TEL in para-toluidine in a paraffin shell. Both TEL and para-toluidine exhibit knock suppressing properties but the use of a para-toluidine as the solids producing agent is not critical to the invention.
U.S. Pat. No. 2,434,650 describes a motor fuel particularly high anti-knock aviation engine fuel of 1943 comprising gasoline hydrocarbon, a knock reducing amount of aromatic amine, a gum inhibiting amount of alkylated hydroxy aromatic oxidation inhibitor free from any amine substituents and a sufficient amount of carbon disulfide to stabilize the aromatic amine present in said fuel against discoloration during storage. The amines employed include the xylidines, the toluidenes, aniline, as well as derivatives of aniline in which either or both of the hydrogens on the amines group are substituted by hydrocarbons. The invention of U.S. Pat. No. 2,434,650 also contemplates the use of metallo-organic anti-knock agents, typically and especially tetraethyl lead (TEL) particularly in preparing high octane aviation motor fuels. In the Examples the fuel comprises 50% naphtha base stock of 75 octane number, 49% high anti-knock hydrocarbon blending agent (alkylate) of 91 octane number, 4 cc TEL/gal and 1% xylidine (mixture of isomers).
U.S. Pat. No. 2,413,262 teaches that the addition of small amounts of primary aromatic amines to aviation-type gasolines of extremely high anti-knock value and containing relatively large amounts of TEL has a definite beneficial effect on the anti-knock characteristics of the fuel so treated. Aviation gasolines having high anti-knock performance are described comprising base aviation gasoline and (a) 0.5 to about 15% of an amine having 7 to 12 carbons of the structure:
in which R1 to R6 inclusive are selected from the group consisting of hydrogen, phenyl, and saturated alkyl; (b) about 1-10 ml/gal of TEL, the TEL additized fuel having an anti-knock rating at least equal to that of 2,2,4-trimethyl pentane (iso octane). Amines include cymidine, p-cumidine, xylidines, with the meta- and para-xylidine being most effective in enhancing the anti-knock qualities of the gasolines containing the aromatic amines. Base fuels have octanes by the CFR motor method of about 75 or above and are suitable for use in high compression internal combustion engines. The formulated/additized fuel has an octane rating of 100+.
U.S. Pat. No. 2,398,197 describes aromatic amine containing gasolines which also contain minor amounts of certain ketones. Aviation gasoline containing aniline or an alkyl aniline plus minor amounts of methyl propyl ketone or methyl isobutyl ketone is identified. The aviation gasoline may contain up to about 6 cc/gal of TEL.
U.S. Pat. No. 1,606,431 describes a motor fuel comprising gasoline (of 1922), benzol and anilene, the aniline being homogeneously blended in the fuel, the aniline being employed at between 0.75 to 1.50 vol %. The level of treatment is not sufficient to boost the low MON aviation gasoline of the 1920's to a MON to 100+.
U.S. Pat. No. 4,321,063 describes liquid hydrocarbon fuels containing anti-knock quantities of benzylic amine compounds. The gasoline is typical automotive gasoline of low motor octane number. Benzylic amine compound will not boost MON of aviation fuel to 100+.
U.S. Pat. No. 4,294,587 describes a liquid hydrocarbon fuel composition containing anti-knock quantities of N-allylic aromatic amines. The gasoline typical automotive gasoline of low motor octane number. N-allylic aromatic amines will not boost MON of aviation fuel to 100+.
In the cited references, critical compression pressure is the maximum cylinder design pressure for which a fuel may be used without knocking. The pressure is tested without the use of fuel. The references focus on maximum fuel efficiency through lean (low fuel-air ratio) operation.
The indicated mean effective pressure (IMEP) achieved according to ASTM D909 by running the fuel as taught in the present case is a measure of the power output attainable by running a rich mixture and is reported in the test in psi. Peak indicated mean effective pressure (PIMEP) is the maximum power output point, and is achieved by varying the air-fuel ratio. The PIMEP in this case is not reliably predicted by the lean fuel-air ratio results as reported in the prior art as critical compression pressure.
It would be desirable to find an additive system for Avgas that will permit formulation of a high octane Avgas having an improved peak IMEP according to ASTM D-909.